S1#erase startup-config
S1#delete flash:vlan.dat 
S1#reload
S1#copy running_config startup-config

interface vlan 1
ip address 192.168.1.2 255.255.255.0
no shutdown

ip default-gateway 192.168.1.1

>enable
#erase startup-config
#delete flash:vlan.dat 
#reload
>enable
#config terminal
#hostname Switch-A
#line console 0
#password cisco
#login
#line vty 0 15
#password cisco
#login
#enable secret cisco
#service password-encryption
#banner motd "Welcome,haha!"
>enable
#config terminal
#ip default-gateway 192.168.1.1
#int vlan 1
#ip address 192.168.1.2 255.255.255.0
#no shutdown
#copy running-config startup-config